It is well known that electrically conductive, fluorine-doped tin oxide layers on glass surfaces decrease the electrical resistance of the coated surfaces as well as increase the infrared reflection. To produce such layers, suitable tin compounds (basic compounds) are brought simultaneously with a fluorine-emitting compound (doping agent) into contact with the glass surface, which has been heated to a temperature of 400.degree. to 800.degree. C. The basic tin compound forms a coherent tin oxide layer on the surface of the glass, the glass ceramic or the enamel. The fluorine from the doping agent increases the electrical conductivity and brings about the high infrared reflection.
Spraying suitable tin-containing and fluorine-containing solutions for applying the fluorine-doped tin oxide layers on the surfaces is technologically very simple.
In the German Offenlegungsschrift 22 46 193, a method is disclosed for preparing transparent, electrically conductive tin oxide films on glass surfaces. For this method, the solution of an organo-tin salt of trifluoroacetic acid in methyl ethyl ketone is used. To prepare the solutions, several expensive steps are required. The tin carboxylates, produced by this method, have a fluorine content, which is too high but specified by the molecular structure. However, excessive doping with fluorine leads to a distinct deterioration in the infrared reflection and the electrical conductivity.
In the German Offenlegungsschrift 39 15 232, a method is disclosed for preparing electrically conductive, IR-reflecting, fluorine-doped tin oxide layers by applying an organic solution of reaction products of trifluoroacetic acid and alkyl tin oxides on the surface heated to a temperature of 400.degree. to 700.degree. C. Ethyl acetate and/or methyl ethyl ketone are used as solvents here. The resulting addition products are, however, not stable. The desirable use of polar, lower alcohols, such as ethanol or isopropanol, as solvents, which, as is well known to those skilled in the art, leads to optically defect-free, uniform layers, is not possible with these compounds.
In the European publication 0 318 486, chloro-tin acetate trifluoroacetates are disclosed. These compounds are synthesized by a multi-step expensive method. The function values of a tin oxide layer, 200 nm thick, produced with these compounds, are of the order of 70% IR-reflection and an electric surface resistance of 40 ohms/square. The main disadvantage of these substances, is however, the presence of chlorine. One of the substances formed during pyrolysis is hydrogen chloride gas, which attacks or damages materials and can endanger health.